1. Field of the Invention
The present invention relates to a novel naphthalene derivative, binaphthalene derivative or biphenyl derivative having oxetane rings capable of being cationically polymerized and a method for producing the same. Photocurable resins and heat curable resins obtained from these derivatives have high refractive indexes and are superior in curability, heat resistance, and mechanical properties, and therefore, can be used in the fields of paints, coating materials, adhesives, lenses, etc. The present invention also relates to a cationically curable compound, which is useful for paint and coating compositions, film and sheet materials, molding materials, sealing materials, adhesives, lenses, etc.
Note that the term xe2x80x9ca derivativexe2x80x9d such as a naphthalene derivative in this specification does not necessarily mean the single compound, but sometimes means plural compounds (i.e., xe2x80x9cderivativesxe2x80x9d).
2. Description of the Related Art
Compounds having oxetane rings (hereinafter sometimes referred to as xe2x80x9coxetane compoundsxe2x80x9d) have come into attention in recent years as monomers capable of being photoinitiative cationically polymerized or cured. Numerous monofunctional and polyfunctional oxetane compounds have been reported. For example, Pure Appl. Chem., A29(10), pp. 915 (1992) and Pure Appl. Chem., A30 (2andamp;3), pp. 189 (1993) disclose methods for synthesis of various oxetane compounds.
Further, DE 1,021,858 discloses an oxetane compound having the following formula: 
wherein R is an aromatic group residue having a valence of 1 or 2 and n is 1 or 2.
Further, Japanese Unexamined Patent Publication (Kokai) No. 6-16804 discloses an oxetane compound having the following formula: 
wherein R represents a hydrogen atom, a C1 to C6 alkyl group, a fluoroalkyl group, an allyl group, an aryl group, a furyl group, a thienyl group, or a fluorine atom, Rxe2x80x2 represents a polyhydric group selected from the group consisting of linear or branched poly(alkyleneoxy) groups, xylylene groups, siloxane bonds, and ester bonds, z represents an oxygen atom or sulfur atom, and m is 2, 3, or 4.
Further, Japanese Unexamined Patent Publication (Kokai) No. 8-245783 discloses numerous oxetane compounds starting from a bifunctional oxetane having a 2,2xe2x80x2-bitolylenediyl skeleton. Further, Japanese Unexamined Patent Publication (Kokai) No. 7-17958 discloses an oxetane compound obtained from the reaction between allyl chloride and hydroxymethyloxetane.
On the other hand, as a naphthalene derivative having an oxetane ring, Bull. Soc. Chim. Fr.; FR; 1965; 694-700 discloses an oxetane compound having the following formula: 
wherein R represents a methyl group or ethyl group.
However, the above derivatives include only one oxetane ring in the molecules thereof, and therefore, are not sufficient for curing with heat or light.
Note that, up until now, no naphthalene derivatives having two oxetane rings in a single molecule as in the present invention have been known.
Furthermore, as a compound capable of curing with an activation energy beam such as ultraviolet light, electron beam, cationically curable compounds having oxetanyl groups (hereinafter referred to as xe2x80x9coxetane compoundsxe2x80x9d) are known. Oxetane compounds are more resistant to oxygen damage, and therefore, superior in the curing as thin films compared with polyfunctional acrylates curing with the same activation energy beams and have the features of toughness, low shrinkage, low skin irritation, etc. as cured articles. Further, they are superior in the copolymerization with epoxy resins generally used, and therefore, can easily provide cured articles having good mechanical strength or bonding (see Japanese Unexamined Patent Publication (Kokai) No. 8-85775 and Japanese Unexamined Patent Publication (Kokai) No. 8-134405).
On the other hand, in the field of optical materials such as lens materials, in recent years resins have come into greater use instead of glass. For example, the rate of use of plastics for eyeglass lenses has reached about 85%. This is because they are light resistant to breakage, and easy to dye as well. Note that, for use as an optical material, the features of a high refractive index, light transmittance, a high Abbe number, and low specific gravity are required, but the high refractive index of resins is particularly important. As a method for improving the refractive index, it is effective to introduce halogen atoms, sulfur atoms, and aromatic rings having large atomic and molecular refractions. However, halogen atoms have the problem of increasing the specific gravity of the resins, while sulfur atoms have the problem of easily generating an unpleasant smell. Further, if an aromatic ring is introduced into the compound, there is the problem that the viscosity of the formulation is increased.
The above oxetane compounds are superior in mechanical strength and bonding and are also superior in terms of high productivity, fine processability, and environmental friendliness, and therefore, can be said to be extremely promising as optical materials. However, if aromatic rings are introduced into the compound to increase the refractive index, the viscosity becomes higher, and therefore, it was extremely difficult to obtain both workability and a high refractive index.
An object of the present invention is to provide a novel naphthalene derivative having two oxetane rings in the single molecule thereof and a method for producing the same.
Another object of the present invention is to provide a novel binaphthalene derivative having two oxetane rings in the single molecule thereof and a method for producing the same.
A further object of the present invention is to provide a novel biphenyl derivative having two oxetane rings in the single molecule thereof and a method for producing the same.
A still further object of the present invention is to provide a cationically curable compound having a low viscosity, superior workability, and high refractive index.
In accordance with the present invention, there is provided a naphthalene derivative having oxetane rings and being represented by the formula (I) or (II): 
wherein R1 and R2 independently represent a hydrogen atom or a C1 to C6 alkyl group.
In accordance with the present invention, there is also provided a method for producing the above naphthalene derivative (I) or (II) having oxetane rings comprising reacting dihydroxynaphthalene with 3-alkyl-3-chloromethyloxetane or 3-chloromethyloxetane in the presence of an alkali metal hydroxide, alkali metal hydride, or alkali metal.
In accordance with the present invention, there is further provided a binaphthalene derivative having oxetane rings and being represented by the formula (III): 
wherein R3 and R4 independently represent a hydrogen atom or a C1 to C6 alkyl group.
In accordance with the present invention, there is still further provided a method for producing the above binaphthalene derivative (III) having oxetane rings, comprising reacting 1,1xe2x80x2-bi-2-naphthol with 3-alkyl-3-chloromethyloxetane or 3-chloromethyloxetane in the presence of an alkali metal hydroxide, alkali metal hydride, or alkali metal.
In accordance with the present invention, there is still further provided a biphenyl derivative having oxetane rings and being represented by the formula (IV): 
wherein R5 to R8 independently represent a hydrogen atom or a methyl group and R9 and R10 independently represent a hydrogen atom or a C1-C6 alkyl group.
In accordance with the present invention, there is still further provided a method for producing the above biphenyl derivative (IV) having oxetane rings, comprising reacting biphenol with 3-alkyl-3-chloromethyloxetane or 3-chloromethyloxetane in the presence of an alkali metal hydroxide, alkali metal hydride, or alkali metal.
In accordance with the present invention, there is still further provided a cationically curable compound comprising (A) a naphthalene derivative having an oxetanyl group and (B) an aromatic compound having an epoxy group or an aromatic compound, other than naphthalene, having an oxetanyl group.
In accordance with the present invention, there is still further provided the above cationically curable compound, wherein said naphthalene derivative (A) having an oxetanyl group is 3-alkyl-3-(1-naphthyloxymethyl)oxetane or 3-(1-naphthyloxymethyl)oxetane and being represented by the formula (V): 
wherein R11 represents a hydrogen atom or a C1 to C4 linear or branched alkyl group.